In March 2011, Naoto Kan, then Japan's prime minister, was caught in the midst of one of the world's worst nuclear crises after a tsunami triggered a reactor meltdown at Fukushima, on the country's eastern seaboard.

At one point he feared he might have to evacuate 50 million people from the Tokyo metropolitan area and surrounding regions.

"Japan as a country would have lost its capability to continue to function for decades afterwards" he said in Darwin on Friday.

Mr Kan, now an avowed opponent of the nuclear industry and an advocate for renewable energy, is beginning a week-long visit to Australia, which will include a trip to the site that supplied some of the fuel for the Fukushima plant – the Ranger uranium mine 250 kilometres east of Darwin .

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On Saturday, he meets the site's traditional owners, the Mirarr people, whose opposition to the mine was over-ridden by a succession of federal governments in the 1970s. Ranger eventually began operations in 1980.

Mine-owner ERA has exhausted deposits at two large open-cut pits and is processing ore it has stockpiled at the site. But it wants to expand the mine underground, to the so-called 3 Deeps deposit, a move that troubles the Mirarr people who fear the environmental impact on the surrounding Kakadu National Park and on their traditional lands.

MR Kan says he wants to learn first hand about the situation at Ranger, having become aware of the debate over its future.

ERA will not disclose its overseas customers, citing commercial confidentiality.

But the World Nuclear Association says Ranger has supplied the nuclear industries of South Korea, China, Britain, France, Germany, Spain, Sweden, and the US as well as Japan.

The risks of expanding the mine's operations were highlighted on December 7 last year, when a so-called leach tank failed, discharging toxic uranium ore leachate over the site.

The federal government suspended Ranger's operations while an inquiry was held, but gave the green light for resumption last month after an interim report found "no adverse environmental impact on human health or Kakadu National Park as a result of the incident",

But a groundwater analysis prepared as part of the investigation conceded there was "insufficient post-spill data to either support or refute that the Leach Tank 1 spill in December last year entered the groundwater underlying the plant."

Over the 34 years of the mine's operation, there have been about 200 incidents of leaks, spills or other breaches of its operating licence, according to the Gundjeihmi Aboriginal Corporation which represents the Mirarr.

NT Environment Centre anti-nuclear campaigner Lauren Mellor says Mr Kan's visit should be a "powerful reminder to the Australian government" to look at weak regulation of the industry and "really re-evaluate our role in that industry".

But the Minerals Council of Australia maintains that the Australian industry remains focused on delivering "world's best practice" in uranium mining.

Despite depressed uranium prices since Fukushima, MCA uranium spokesman Daniel Zavattiero said there was likely to be strong demand in future from China and India as they battled air pollution and tried to meet growing energy demand.